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represents a launch or test day, and describes the
events that took place.
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This is a new rocket made out of
three 1.25L bottles. It is our
tallest rocket to date. Parachute
deployment is achieved using the
nose-cone-off-at-apogee technique.
Rocket is typically filled with 1.1
liters of water.

Frankovka III

4
L

This is an older rocket designed to
carry a video camera and a flight
computer. On this day, it was flown
with the camera and the flight computer
for the first time. This is a 2 x 2L
rocket. Typical fill is 1.25L of
water.

Team Members at
Launch Event:
PK, GK, Paul K and John K.

Number
of launches: 9

It's only been a couple of days since the
last launch day, but we were keen to fly the
newly repaired J4Y rocket. It wasn't a
perfect day for flying because there was the
occasional light shower, but at least the
air was fairly still.

Flight Day Events

J4Y was first up with a 9mm nozzle,
filled to 110psi without any more leaks.
The flight was excellent, with a
parachute deployment right near apogee.

J4Y was flown 5 times on the day
with pressures up to 135 psi with no
issues on the pressurisation side of
things, however, parachute deployment
was a little off. The parachute tended
to deploy too early on the rocket, but
thanks to the strong main chute line and
the hole in the parachute, crashes were
avoided.

Frankovka III was flown 4 times,
once with a video camera. The flight
looked great, and we were looking
forward to the video footage, but when
we tried to download it from the camera,
the computer said the file was corrupt.
We could see that the file wasn't full
length but all our attempts to read it
failed. What we believe happened was
that the impact with the ground, even
though it was a parachute landing, was
too great and it either jarred the
camera switch or likely the power was
briefly interrupted. This would have
certainly corrupted the file mid
recording.

On the previous day when we recorded in
flight video, the video too was cut
short on landing. but we were able to
recover the file without problem. We
will attempt to address this issue in
three ways. More padding for the camera,
bigger chute and have the rocket land
tail first to try to reduce the shock
from the landing.

Frankovka III has been flying really
well, but we have noticed on a number of
occasions the rocket tilts significantly
just after takeoff (see picture on the
left), and then tends to
reverse the direction just before the
air-pulse. After that the rocket appears
to fly quite straight, and not
spiralling, which leads us to believe
that it isn't the aerodynamics of the
rocket. At first we thought perhaps a
fin was bending under acceleration, but
this would be less likely to happen
within the first 5 meters of take-off
when speeds are still comparatively low.
A faulty misaligned nozzle could cause
this as we have seen it in the past, but
the in those instances the rocket tended
to continue to turn in the same
direction for the entire boost phase.

We suspect it is caused by the water
creating a wave inside the bottle, as
others have mentioned on various forums.
Perhaps as the rocket is leaning
slightly to one side on the launch pad,
there is more water on one side of the
bottle, as the rocket accelerates, the
acceleration forces the water level to
become perpendicular to the water flow
from the nozzle creating a wave. This movement of water
could explain the sudden shift in
direction just after takeoff. It could
also explain the reason why the rocket
looks like it reverses the direction of
tilt before the water runs out. This
could be caused by the wave reflecting
off the other side of the bottle. When
the water runs out there is no more
instability issue and the rocket flies
straight. We will try some experiments
to see if this is the cause.

Potential ways of reducing this effect
would be to make sure the rocket is
perfectly vertical on the launch pad,
and perhaps some kind of baffles to stop
the water from sloshing around inside.
Probably the first test will be to use
detergent to create foam inside the
bottle to reduce the wave action. Foam
inside of water rockets isn't anything
new, and
Antigravity research have used
it on their world record attempts.

Flight Record

Launch

Rocket

Pressure (PSI)

Notes

1

J4Y

110

9mm nozzle.
Excellent flight, with parachute
deploying right near apogee.

2

J4Y

120

7mm nozzle. Straight
flight, slow take off.

3

Frankovka III

130

Flown with video
camera, rocket went straight up.
Computer was set at the 4.5 second
deploy setting. Video footage was
corrupted on landing.

4

Frankovka III

135

No video camera,
4.75 second deploy setting on FC.
The rocket angled considerably on
take off before proceeding to fly
long and straight although be it at
an angle. The rocket landed in some
trees, but was easily shaken down.

5

J4Y

130

9mm nozzle, Take off
was straight up, but the parachute
deployed way too early, the momentum
of the nosecone, ripped it off from
where it was attached to the rocket.
Rocket landed safely.

6

J4Y

130

9mm nozzle, Good
straight take off, but the parachute
opened too early again. The rocket
drifted back to the launch site and
actually hit the launcher when it
landed.

7

Frankovka III

135

9mm nozzle. The
rocket angled quite a bit on
take-off. The parachute looked like
it took a little too long to deploy.
Perhaps it took a while to open.

8

Frankovka III

135

Perfect flight
straight up. The rocket looked like
it drifted for quite a long time.
Flight time was 29 seconds.

9

J4Y

135

Good flight, but the
parachute opened way too early
again.

Design and Development

When using the nosecone off at
apogee (or any time in between launch
and lawndart) technique we find we have
to do a certain amount of tuning to get
it just right. We will now be building
the next iteration of the flight
computer (FC) for the J4Y rocket. The
aim is to have the FC lighter and
smaller for a good fit into the 90mm
rocket diameter.

Since a rocket finally got stuck in a
tree, we have been thinking of ways to get
them down. Some ideas were: have the FC cut
the chute line; have the FC release a long
string with a weight to the ground so it can
be pulled down; or my favourite - have the
parachute on a very long line, that way the
rocket dangles lower to the ground where it
is easier to reach.